A variety of rowing machines exist for physical fitness of rowers and for fitness training in general. The three most influential rowing machines developed in the last 40 years are the Gamut Erg machine, the Gjessing Erg machine and the CONCEPT2® machine. The Gamut Erg and Gjessing Erg machines are no longer produced, but the CONCEPT2® machine is currently produced and has become the predominant rowing machine, especially for the physical conditioning of rowers of competitive rowing crews. Various competitors of the makers of the CONCEPT2® machine have incorporated numerous aspects of the CONCEPT2® machine into their machines. Other machines currently on the market include the Row Perfect, STAMINA®, Body Track, Life Care, KETTLER®, and Water Rower machines, among others.